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Update to match reality. Give more indepth description of SCB paging
and tagged queueing. Mention the AHC_ALLOW_MEMIO option.
This commit is contained in:
Justin T. Gibbs
parent
df98fb1bb2
commit
2e3507efc7
Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=22897
@ -1,5 +1,5 @@
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.\"
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.\" Copyright (c) 1995, 1996
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.\" Copyright (c) 1995, 1996, 1997
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.\" Justin T. Gibbs. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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@ -40,18 +40,21 @@ For one or more PCI cards:
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.Cd controller pci0
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.Cd controller ahc0
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.Pp
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To enable SCB paging:
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.Cd options AHC_SCBPAGING_ENABLE
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.Pp
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To enable tagged queueing:
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.Cd options AHC_TAGENABLE
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.Pp
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To enable SCB paging:
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.Cd options AHC_SCBPAGING_ENABLE
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To allow PCI adapters to use memory mapped I/O if enabled:
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.Cd options AHC_ALLOW_MEMIO
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.Pp
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For one or more SCSI busses:
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.Cd controller scbus0 at ahc0
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.Sh DESCRIPTION
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This driver provides access to the
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.Tn SCSI
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bus connected to an Adaptec
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bus(es) connected to Adaptec
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274x, 284x, 2940, 3940, or controllers based on the
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.Tn AIC7770,
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.Tn AIC7850,
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@ -65,23 +68,65 @@ ultra
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.Tn SCSI,
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two active commands at a time per non-tagged queueing target,
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tagged queuing,
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and SCB paging which allows up to 255 active commands on all adapters
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except those using
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.Tn AIC7770
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chips prior to revision E.
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Tagged queueing is enabled with the
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.Dq Dv AHC_TAGENABLE
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configuration option.
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and SCB paging.
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.Pp
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The number of concurrent transactions allowed is chip dependent
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and ranges from 3 to 16.
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On PCI adapters,
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this number can be increased with the SCB paging option.
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SCB paging implements an algorithm to 'page-out' transactions
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that are in the disconnected state so that the freed space in
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the controller's memory can be used to start additional transactions.
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On the aic7880 and aic7870,
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this increases the maximum number of outstanding transactions from 16 to 255.
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On the aic7850 and aic7860 controllers, this maximum rises from 3 to 8.
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During the hardware probe,
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a diagnostic showing the ratio of hardware supported 'slots' to number
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of transactions is printed.
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SCB paging is enabled with the
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.Dq Dv AHC_SCBPAGING_ENABLE
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configuration option.
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This option will likely be removed and become the default behavior for
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adapters that support it,
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in the near future.
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.Pp
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Tagged queueing is enabled with the
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.Dq Dv AHC_TAGENABLE
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configuration option.
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Tagged queueing allows multiple transactions to be queued at the device
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level instead of the host level,
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allowing the device to re-order I/O to minimize seeks,
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seek distance,
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and to increase throughput.
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Tagged queueing can have a significant impact on performance for seek
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bound applications and should be enabled for most configurations.
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Unfortunantly, some devices that claim to support tagged queueing fail
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miserable when it is used.
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The only reason tagged queueing remains as a controller option is as a
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stop gap measure until a mechanism to detect these broken devices and to
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control this feature on a per device basis is in place.
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.Pp
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Memory mapped I/O can be enabled with the
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.Dq Dv AHC_ALLOW_MEMIO
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configuration option.
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Memory mapped I/O is more efficient than the alternative, programmed I/O.
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Most PCI BIOSes will map devices so that either technique for communicating
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with the card is availible.
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In some cases,
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usually when the PCI device is sitting behind a PCI->PCI bridge,
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the BIOS fails to properly initialize the chip for memory mapped I/O.
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The symptom of this problem is usually a system hang if memory mapped I/O
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is attempted.
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Most modern motherboards perform the initialization correctly and work fine
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with this option enabled.
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.Pp
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Per target configuration performed in the
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.Tn SCSI-Select
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menu, accesible at boot
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in
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.No non- Ns Tn EISA
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models or through an
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models,
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or through an
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.Tn EISA
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configuration utility for
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.Tn EISA
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@ -109,15 +154,12 @@ cards.
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Some Quantum drives (at least the Empire 2100 and 1080s) will not run on an
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.Tn AIC7870
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Rev B in synchronous mode at 10MHz. Controllers with this problem have a
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42 MHz clock crystal on them and run slightly above 10MHz, causing the
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42 MHz clock crystal on them and run slightly above 10MHz. This causes the
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drive much confusion. Setting a maximum synchronous negotiation rate of 8MHz
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in the
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.Tn SCSI-Select
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utility
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will allow normal function.
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.Pp
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The code to perform SCB paging doesn't work properly, don't use this option
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at this time.
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.Sh SEE ALSO
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.Xr aha 4 ,
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.Xr ahb 4 ,
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@ -1,5 +1,5 @@
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.\"
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.\" Copyright (c) 1995, 1996
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.\" Copyright (c) 1995, 1996, 1997
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.\" Justin T. Gibbs. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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@ -40,18 +40,21 @@ For one or more PCI cards:
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.Cd controller pci0
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.Cd controller ahc0
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.Pp
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To enable SCB paging:
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.Cd options AHC_SCBPAGING_ENABLE
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.Pp
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To enable tagged queueing:
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.Cd options AHC_TAGENABLE
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.Pp
|
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To enable SCB paging:
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.Cd options AHC_SCBPAGING_ENABLE
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To allow PCI adapters to use memory mapped I/O if enabled:
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.Cd options AHC_ALLOW_MEMIO
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.Pp
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For one or more SCSI busses:
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.Cd controller scbus0 at ahc0
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.Sh DESCRIPTION
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This driver provides access to the
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.Tn SCSI
|
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bus connected to an Adaptec
|
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bus(es) connected to Adaptec
|
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274x, 284x, 2940, 3940, or controllers based on the
|
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.Tn AIC7770,
|
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.Tn AIC7850,
|
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@ -65,23 +68,65 @@ ultra
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.Tn SCSI,
|
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two active commands at a time per non-tagged queueing target,
|
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tagged queuing,
|
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and SCB paging which allows up to 255 active commands on all adapters
|
||||
except those using
|
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.Tn AIC7770
|
||||
chips prior to revision E.
|
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Tagged queueing is enabled with the
|
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.Dq Dv AHC_TAGENABLE
|
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configuration option.
|
||||
and SCB paging.
|
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.Pp
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The number of concurrent transactions allowed is chip dependent
|
||||
and ranges from 3 to 16.
|
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On PCI adapters,
|
||||
this number can be increased with the SCB paging option.
|
||||
SCB paging implements an algorithm to 'page-out' transactions
|
||||
that are in the disconnected state so that the freed space in
|
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the controller's memory can be used to start additional transactions.
|
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On the aic7880 and aic7870,
|
||||
this increases the maximum number of outstanding transactions from 16 to 255.
|
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On the aic7850 and aic7860 controllers, this maximum rises from 3 to 8.
|
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During the hardware probe,
|
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a diagnostic showing the ratio of hardware supported 'slots' to number
|
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of transactions is printed.
|
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SCB paging is enabled with the
|
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.Dq Dv AHC_SCBPAGING_ENABLE
|
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configuration option.
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This option will likely be removed and become the default behavior for
|
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adapters that support it,
|
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in the near future.
|
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.Pp
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Tagged queueing is enabled with the
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.Dq Dv AHC_TAGENABLE
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configuration option.
|
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Tagged queueing allows multiple transactions to be queued at the device
|
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level instead of the host level,
|
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allowing the device to re-order I/O to minimize seeks,
|
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seek distance,
|
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and to increase throughput.
|
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Tagged queueing can have a significant impact on performance for seek
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bound applications and should be enabled for most configurations.
|
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Unfortunantly, some devices that claim to support tagged queueing fail
|
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miserable when it is used.
|
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The only reason tagged queueing remains as a controller option is as a
|
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stop gap measure until a mechanism to detect these broken devices and to
|
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control this feature on a per device basis is in place.
|
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.Pp
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Memory mapped I/O can be enabled with the
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.Dq Dv AHC_ALLOW_MEMIO
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configuration option.
|
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Memory mapped I/O is more efficient than the alternative, programmed I/O.
|
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Most PCI BIOSes will map devices so that either technique for communicating
|
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with the card is availible.
|
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In some cases,
|
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usually when the PCI device is sitting behind a PCI->PCI bridge,
|
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the BIOS fails to properly initialize the chip for memory mapped I/O.
|
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The symptom of this problem is usually a system hang if memory mapped I/O
|
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is attempted.
|
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Most modern motherboards perform the initialization correctly and work fine
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with this option enabled.
|
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.Pp
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Per target configuration performed in the
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.Tn SCSI-Select
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menu, accesible at boot
|
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in
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.No non- Ns Tn EISA
|
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models or through an
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models,
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or through an
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.Tn EISA
|
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configuration utility for
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.Tn EISA
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@ -109,15 +154,12 @@ cards.
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Some Quantum drives (at least the Empire 2100 and 1080s) will not run on an
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.Tn AIC7870
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Rev B in synchronous mode at 10MHz. Controllers with this problem have a
|
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42 MHz clock crystal on them and run slightly above 10MHz, causing the
|
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42 MHz clock crystal on them and run slightly above 10MHz. This causes the
|
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drive much confusion. Setting a maximum synchronous negotiation rate of 8MHz
|
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in the
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.Tn SCSI-Select
|
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utility
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will allow normal function.
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.Pp
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The code to perform SCB paging doesn't work properly, don't use this option
|
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at this time.
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.Sh SEE ALSO
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||||
.Xr aha 4 ,
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||||
.Xr ahb 4 ,
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||||
|
||||
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